1. Field of the Invention (Technical Field)
The embodiments of the present invention relate to pipe inspection and more particularly to a method and apparatus for using and controlling a crawler to inspect the integrity of installed pipes.
2. Background Art
Pipelines are used around the world to transport fluids for a multitude of applications including refineries and power plants. The failure of these pipelines can cause not only a loss of the transported fluid but also injury to persons and the environment. Thus, the integrity of the pipelines must be periodically checked to avoid failures. Unfortunately, the pipes cannot be visually inspected because the failures are due to internal damage and secondly pipelines usually have an insulating layer disposed on the pipe preventing any type of visual inspection. These failures are caused by deterioration over time due to erosion or corrosion. Various methods have been used to measure the thickness of the pipes to predict or detect possible failures. These methods include ultrasonic, x-ray and gamma ray detection methods. An apparatus or vehicle is necessary to apply these detection methods in the field. These vehicles need to operate on a variety of different sized pipes, pipes in many configurations and in some cases, must survive extreme environmental conditions. In addition, the vehicle must be easy to operate with minimal assistance and without highly qualified or technical support.
There are presently two types of vehicles used for failure detection. The first is a vehicle that is inserted into the pipe and travels along the interior of the pipe. These devices are discussed in U.S. Pat. No. 4,435,829 and U.S. Pat. No. 3,764,806. These systems have several obvious disadvantages, such as inserting the vehicle and gathering the data that is generated. The fluid delivery is usually curtailed or stopped during measurements. The second type of system is the provision of a vehicle that travels along side of the exterior of the pipe, as discussed in US Patent Application No. 2006/0078091A1 or vehicles that encase or travel on the pipe. U.S. Pat. No. 5,698,854 describes a vehicle that travels on the apex of a pipe to carry pipe analysis equipment. This system uses one or two motors to drive the vehicle on the pipe, but does not teach or imply any type of stabilization or steering system. The device merely is driven down the pipe with a motor driving the front wheels and a separate motor driving the rear wheels. Currently, most vehicles for carrying the detection devices use outrigger supports to stabilize the crawler's movements. The supports include a separate wheel mechanism on an adjoining pipe or on a separate vehicle traveling on the ground in order to keep the vehicle near the apex of the pipe during operation. If the crawler is not located precisely at the apex, a center referenced scan will not be obtained. Without the use of outriggers, the crawler will bind or fall off the pipe, causing significant delays in inspections. This methodology for stabilizing and controlling the crawler's movements, limits the functionality to only straight pipeline sections. Any bends/corner sections of the pipeline cannot be tested. Further, partial disassembly and reassembly of the vehicle components is required at every support junction of the pipeline. Using these prior art systems the vehicle can only be approximately positioned at the vertex of the pipe. Disassembly and reassembly significantly reduces the amount of productivity with regard to the total amount of time required to perform an inspection from start to finish.
The main disadvantage of current technology is the need for external supports to help guide the crawler down the pipeline. The current drive method uses a linear DC voltage supply to drive both motors at approximately the same speed. Linear DC voltage supplies are very large and heavy, so it is required to carry the supply in a truck with the operator that is analyzing the corrosion data. No adjustment on wheel angle was utilized for traction enhancement of driver wheels resulting in frequent slippage, which is detrimental to final scan quality. Scanning equipment brackets must be disassembled at each vertical pipe support crossing. Using extraneous equipment, the external supports, requires a significant amount of time to setup and provide no benefit to the actual corrosion data being analyzed. This method requires more equipment than needed, a longer setup and break down time, and data measurements that are never oriented to a true vertical. This setup also causes unbalanced wear on the system.
A constant positioning and realignment control loop system is necessary to solve the problems outlined above and is essential to maintain positioning on the apex of the pipe. This gives an accurate mapping of the corrosion damage. Drive wheel traction remains a problem in previous designs. Substantial time is required for disassembly and re-assembly of scanning equipment. The current crawlers will bind or drive off the pipeline. Because of this the current setup cannot function without the use of external guides, or outrigger supports. The present invention requires minimal setup and no external supports. The present invention has the ability to cross over supports without significant disassembly which allows for considerable improvements in process productivity. Further, curved sections of pipe that were previously unable to be inspected can be checked giving a significant amount of inspection coverage that was not possible in the prior art.